"This study provides further evidence that in some children, prenatal exposure to SSRIs may influence their risk for developing an autism spectrum disorder," Hertz-Picciotto said. "It also highlights the challenge for women and their physicians, to balance the risks vs. benefits from taking these medications, given that a mother’s underlying mental-health conditions may also pose a risk to both herself and her child.”

The study participants included the mothers of children with autism spectrum disorder (ASD), developmental delay (DD) and those with typical development (TD). The children ranged in age from 2 to 5. A majority of the children in each category were boys — 82.5 percent of those with ASD, 65.6 percent with DD and 85.6 percent TD.

While the study included girls, the substantially stronger effect in boys suggests a possible gender difference in the effect of prenatal SSRI exposure, the authors said.

“We found prenatal SSRI exposure was nearly three times as likely in boys with ASD relative to those with typical development, with the greatest risk occurring when exposure took place during the first trimester,” said Li-Ching Lee, psychiatric epidemiologist in the Bloomberg School’s Department of Epidemiology. “SSRIs also were elevated among boys with developmental delay, with the strongest exposure effect in the third trimester.”

According to statistics recently released by the U.S. Centers for Disease Control and Prevention, an estimated 1 in 68 U.S. children are diagnosed with ASD. The condition is almost five times more commonplace among boys than girls. The researchers caution that while there has been a co-occurring increase in the use SSRIs, it likely is not a significant contributor to the increase in the prevalence of autism.

“Because of low rates of SSRI use during pregnancy and possible co-existing factors influencing susceptibility to ASD from SSRI exposure, any contribution of these medications to the increase in the prevalence of ASDs likely is minimal,” Lee said.

Maternal depression carries its own risks to the fetus, so that the benefits of using SSRIs during pregnancy should be weighed carefully against any potential harm, the authors noted. They also noted that large sample studies are needed to investigate the effects in girls with ASD.

The study's limitations include the difficulty of isolating SSRIs' effects from those of their indications for use; lack of information on SSRI dosage precluding dose-response analyses, and the relatively small sample of children with developmental delay resulting in imprecise estimates of association.

The study is funded by the National Institute of Environmental Health Sciences grants P01-ES11269, R01-ES015359, the UC Davis MIND Institute and Autism Speaks.

At the UC Davis MIND Institute, world-renowned scientists engage in collaborative, interdisciplinary research to find the causes of and develop treatments and cures for autism, attention-deficit/hyperactivity disorder (ADHD), fragile X syndrome, 22q11.2 deletion syndrome, Down syndrome and other neurodevelopmental disorders. For more information, visit mindinstitute.ucdavis.edu